Process and device for producing hollow bodies

ABSTRACT

A device and method are disclosed for the production of hollow bodies, especially plastic bottles, wherein a section of a plastic flexible hose is placed in a cavity of a blow mold by an extruder head according to a predefined clocked pulse. The plastic flexible hose is inflated inside the blow mold by a blow mandrel by overpressure according to the blow mold cavity. The manufactured inflated hollow body is subsequently removed from the mold. The plastic hose can be continually held on opposite sides of the blow mold arrangement during the entire extrusion and blow cycle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 10/547,192filed on May 5, 2006, which is a U.S. national stage application ofInternational Application No. PCT/CH2004/000047 filed on Jan. 29, 2004and which claims priority to Swiss Application Nos. 341/03 filed on Mar.5, 2003 and 517/03 filed on Mar. 25, 2003, the entire contents of whichare incorporated herein by reference.

BACKGROUND

Containers which were conventional in the past and which made of whiteor colored sheet metal, glass or also ceramic are being increasinglydisplaced by plastic containers. Mainly plastic containers are used forpackaging of fluid substances, for example beverages, oil, cleaningagents, cosmetics, etc. The low weight and lower costs play a notinsignificant part in this substitution. The use of recyclable plasticmaterials and overall more favorable total energy balance in theirproduction also contribute to promoting the acceptance of plasticcontainers, especially plastic bottles, among consumers.

The production of plastic containers, especially plastic bottles, forexample from polyethylene or polypropylene, takes place in an extrusionblowing process, especially in a process of blowing extruded tubes. Indoing so a plastic tube is extruded from an extruder head, placed inblow molding tools, inflated by way of a blowing mandrel byoverpressure, and hardened by cooling. The extrusion blowing machinesused for this purpose generally have at least one extruder for supply ofthe plastic material. The output of the extruder is connected to theextruder head and on its discharge nozzle which can preferably beregulated in opening width an extruded tube or one extruded in severallayers emerges. The extruded tube is transferred to a blow molding tooland inflated within its cavity with a blowing mandrel. The plastic tubecan have one or more layers, it can be extruded as a tube with visualstrips, decorative strips, or, relative to the periphery, with severalsegments for example of different colors.

The blowing station with the blowing mandrel is conventionally locatedlaterally from the extrusion head and the blow molding tool which issupplied with the extruded tube must be moved into the blowing stationwhere then the blowing mandrel is conventionally transported fromoverhead into the blow molding cavity. For continuous operation in onetype of known extrusion blowing machines, there are conventionally twoblowing stations. Each blowing station is equipped with one blow moldingtool. The blowing stations are located opposite one another on eitherside of the extruder and have blow molding tables with the blow moldingtools which are moved alternately under the extruder head in order toreceive the extruded tube. In doing so the blow molding tool is openedfor retrieving the tube. After closing the blow molding tool the tube iscut off between the extrusion head and the blow molding tool. Afterwardsthe blow molding table is moved again into the blowing station, wherethe blowing mandrel is transported into the cavity of the blow moldingtool and the tube is inflated according to the blow molding cavity andafterwards removed. For multiple extrusion heads and multiple blowmolding tools each blowing station is equipped with a correspondingnumber of blowing mandrels which are jointly transported into the blowmolding cavities. Altogether the extruder with the extruder head and thetwo blow molding stations form roughly the shape of a T. The extruderwith the extruder head constitutes the long leg of the T, while the twoblowing tables can be moved alternately along the short crosspiecehalves to under the extruder head.

Extrusion blowing machines of the above described type have been testedand allow high production performance. But there is still a desire forimprovements in order to further reduce the required tool investments,i.e. the costs per blow molding cavity. The necessity of moving the blowmolding tables with the blow molding tools laterally to the blowingstations leads to dead times which result from the path to be traversedand the speed of motion of the blow molding tables. Due to therelatively great masses which must be accelerated and braked again, thespeed of motion can not be selected to be optionally large. Also thepaths to be traversed laterally cannot be further shortened forconstruction reasons. The extruded tube must be cut off after the blowmolding tool is filled. This conventionally takes place by a laterallysupplied cutting blade. The tube part which continues to be extruded andwhich projects from the extrusion nozzle swings back and forth after thecutting process. In particular, for very high clock cycles the swingingof the tube can lead to problems in the transfer of the tube to the blowmolding cavity.

Extrusion blowing machines are known in which a number of blow moldingtools are located on a rotating wheel. The wheel stands roughlyvertically and guides the blow molding tools roughly tangentially to theplastic tube which has been continuously extruded by the extrusion head.Shortly before reaching the extruded plastic tube, the guided blowmolding tool is opened to retrieve the tube. As the wheel continues toturn, the blow molding tool is closed around the inserted tube and thelatter is finally cut off during further turning. The arrangement of theblow molding tools and the speed of rotation of the wheel are chosensuch that the tube is only cut off when the following blow molding toolhas closed around the next tube piece. The tube which is located in thecavity of the blow molding tool as the wheel continues to turn finallytravels into the blowing station where it is inflated by way of ablowing mandrel which is inserted laterally into the mold tool accordingto the blow molding cavity. Finally, the inflated hollow body isdischarged from the blow molding tool by opening. The blow molding toolwhich is located on the rotating wheel is closed again as motioncontinues and is moved again to the extrusion head in order toaccommodate another extruded tube.

The disadvantage in the wheel blowing machines is the circumstance thatdue to the large number of separate blow molding tools located on thewheel, they require a relatively high investment cost for preparation ofthe blow molding tools. In general the blow molding tools are notcompletely identical. This can lead to quality differences in themanufactured hollow bodies from blow molding tool to blow molding tool.The use of blow molding tools with several blow molding cavities isrelatively difficult and expensive. The blow molding tools can only beattached at fixed mounting points on the wheel. They are fixed accordingto the height of the blown hollow body which can be produced at maximumwith the machine. The mounting points, once established, can no longerbe changed. This is also a result of the mechanical controls which areconventional in these machines via control cams, cam disks and the like.If containers with a smaller height are to be blown on the wheel blowingmachine, the smaller blow molding tools mounted on the periphery of thewheel have a greater angular distance from one another. Since theplastic tube emerges continuously from the extrusion head, this leads tolarger amounts of scrap in the areas between the two blow molding tools.The extruded plastic tube is accepted by the blow molding tool which hasmoved past along a circular shape under the extrusion head. Arc motionis superimposed on the lateral feed motion of the closing blow moldhalves. By a radius of the wheel as large as possible, the attempt ismade to keep this arc motion of the blow mold halves as small aspossible when the plastic tube is being accepted; but it cannot becompletely eliminated. The circumstance that the tube between twosuccessive blow molding tools on the one hand is held by the extruderhead and on the other hand by the advancing blow molding tool, cannotchange anything in the geometrical relationships. Under certaincircumstances therefore for more complex container geometries it canoccur that the tube is not ideally inserted into the blowing cavity andis partially pinched between the adjoining areas of the closing blowmold halves. This can lead to unwanted scrap.

SUMMARY

A blow molding process and an extrusion blowing machine will be devisedwhich allow reliable processing of different raw plastic products. Withrespect to the configuration of the container geometries there should beas much free space as possible, and containers with very complexgeometry with very narrow specifications will also be producible. In theproduction of critical container geometries or thin-walled containersproduction reliability as high as possible is to be ensured. The processand device for extrusion blowing of hollow bodies will be compatible forproduction of large and small geometries. Unnecessary scrap is to belargely avoided. The process and the device are to be modified such thatregardless of the number of cavities per blow molding tool, largelyidentical container properties and quality parameters will be achieved.The adjustment data determined in the test will be largely applicableunchanged to production plants. The space requirement compared toexisting machines should not be greater, it should even be possible toreduce it. Dead times as occur in known machines when the blow moldingtools move sideways into the blowing stations will be reduced.

In the process for producing hollow bodies, especially plastic bottles,a segment of a plastic tube is placed in a cavity of a blow molding toolby the extruder head in a definable cycle. Within the blow molding toolthe plastic tube is inflated via a blowing mandrel by overpressureaccording to the blow molding cavity. The finish-blown hollow body isfinally removed from the mold. As claimed in the invention the plastictube is continuously held during the entire extrusion and blowing cycleon the opposing sides of the blow molding tool arrangement.

In the process as claimed in the invention the plastic tube iscontinuously held during an entire production cycle, i.e. during theentire extrusion and blowing cycle, on opposite sides of the blowmolding tool arrangement. In this way the plastic tube is permanentlyguided and faulty positions can be avoided. This establishes theprerequisite for always placing a tube which has been extruded from anextrusion nozzle in the same blow molding cavity. All the hollow bodiesproduced with an extrusion nozzle-blow molding cavity arrangement aresubject to the same adjustment and tool parameters in this way. Qualitydifferences as a result of blow molding cavity tolerances of differentsizes in arrangements with several different blow molding tools areeliminated. Dead times which take place by lateral displacement of theblow molding tool arrangement relative to the extruder head areeliminated, since the blow molding tool arrangement is alignedessentially only to the transport direction of the plastic tube. Theplastic tube which is located in the blow molding cavity is inflatedimmediately after feed of the blow molding cavity with an extrudedplastic tube. The plastic tube is kept in a defined position during theentire extrusion and blowing cycle and can no longer swing around itsaxis. The extruder head and the blow molding tool arrangement during theentire extrusion and blowing process remain in a definable andadjustable, geometrical positional relationship, and the plastic tubecan always be optimally accepted. In this way, for complicatedgeometries of the blow molding cavity the danger of unintentionalpinching of the plastic tube is reduced. The process guidance as claimedin the invention makes it possible if necessary to change in a concertedmanner the location of the extruded plastic tube with reference to theblow molding cavity in order to take into account special geometricalrequirements.

In one advantageous version of the process as claimed in the invention,the plastic tube is cut off only after complete inflation of the hollowbody. The cutting-off can take place by controlled squeezing off orshearing off. Preferably a cutting blade or the like is used for thispurpose. This process version differs both from the blowing process withthe known wheel blowing machines in which the tube is sheared offessentially uncontrolled after acceptance by the blow molding tool asthe wheel continues to turn, and also from the continuous anddiscontinuous blowing process with known extrusion blowing machines inwhich the plastic tube is cut in a controlled manner before the actualblowing process. The process guidance as claimed in the inventionresults in that the blowing mandrel must be synchronized for a certaintime with the motion of the extruder head and/or the extrusion ortransfer speed of the plastic tube to the blow molding tool arrangement.This simple measure however ensures that the tube is held in acontrolled manner in each phase of the production cycle.

Separation of the plastic tube takes place advantageously on the side ofthe blow molding tool arrangement facing way from the extruder head. Inthis way the guidance of the tube over the finish-inflated hollow bodywhich is located on the blowing mandrel and over the extruder head isensured before cutting off. The tube material scrap can always be keptas small as possible regardless of the height of the blow molding cavityby the arrangement of the point of separation in the immediate vicinityof the mouth of the blow molding cavity.

With reference to the direction of motion of the plastic tube, the blowmolding tool means is located between the extruder head and the blowingmandrel. The blowing mandrel is transported through the mouth of theblow molding cavity which is located on the side of the blow moldingtool arrangement facing away from the extrusion nozzle. The output ofthe extrusion nozzle and the axial extension of the blowing mandrel arearranged such that they are essentially axially flush.

In one version of the invention, to reduce the dead times for each blowmolding cavity there are two or more blowing mandrels. The blowingmandrels can be for example located next to one another and can suppliedin alternation to the openings. In one alternative version severalblowing mandrels are attached to the central blowing mandrel supportsuch that they are used in succession by rotation of the blowing mandrelsupport. For example, the blowing mandrel support can carrying twoblowing mandrels which are opposite one another offset by 180°. In thisversion, after inflating the tube and opening the blow molding toolarrangement the blowing mandrel support is turned by 180°. The secondblowing mandrel is thus already prepared for inflation of another tubesection while the hollow body on the first blowing mandrel still waitsfor its removal. It goes without saying that there can also be rotaryblowing mandrel supports with 3, 4 or more blowing, mandrels. The angleby which the blowing mandrel support must continue to be turned derivesfrom the division of 360° by the number of blowing mandrels.

The arrangement on the side of the blow molding tool arrangement facingaway from the extrusion nozzle also offers the possibility of providingeach blowing mandrel with a calibration means with which the opening ofthe blown hollow body is calibrated during the blowing process. In thisway a separate finishing station in which this process must be repeatedis eliminated.

In a continuous extrusion blowing process, the plastic tube iscontinuously extruded from the extrusion nozzle of the extruder head.After transfer of the extruded plastic tube to the blow molding cavityand during the entire blowing process, the relative distance of theextruder head from the blow molding tool arrangement is increased sothat during further extrusion it does not strike the surface of the blowmolding tool arrangement and the tube can be kept in a controlledalignment. This takes into account the circumstance that the plastictube is continuously extruded from the extrusion nozzle while theinflation process in the mold cavity of the blow molding toolarrangement is a discontinuous process.

The relative change in the distance between the extruder head and theblow molding tool arrangement takes place at least with a speed whichcorresponds to the exit speed of the plastic tube from the extrusionnozzle. This ensures that the extruded tube does not run onto thesurface of the blow molding tool arrangement. In the choice of a higherrate of change of the distance than the extrusion speed, the plastictube which is clamped in areas in the blow molding tool arrangement ispulled therefore out of the nozzle tool. In this way for example thewall thickness of the extruded plastic tube can be changed in aconcerted manner. A thin-walled tube can thus be produced with arelatively large nozzle gap. On the one hand this has the advantage thatin spite of the high throughput the pressure in the extruder head can bekept comparatively low, and on the other hand the dissipation and thusthe temperature increase in the tube become less. Another advantage isthat even when processing highly swelling materials a thin-walled tubecan be produced, since as a result of the larger nozzle gap and theassociated lower shear the danger of a melt rupture is reduced. It canalso be provided that the relative speeds between the extruder head andthe blowing mandrel or blow mold during continuous tube discharge arechanged continuously according to an stretching program in order toinfluence the tube wall thickness to the desired degree.

To achieve a change in distance between the extruder head and the blowmolding tool arrangement, it is possible to move the extruder head orthe blow molding tool arrangement away or to carry out a combination ofthe two movements. The adjustment of only one of the two equipment partssimplifies the construction and the control of the sequences of motion.For considerations of construction it is advantageous if the change inthe distance takes place only by moving the extruder head away relativeto the blow molding tool arrangement which is stationary with respect toits location. On the one hand, in the area of the extruder head there ismore space for mounting of lifting means. On the other hand, it isadvantageous for the feed of the blowing mandrel if the blow moldingtool arrangement retains its position essentially unchanged during theentire blowing cycle. The blow molding tool arrangement must executeonly one opening and closing motion for accommodating the tube sectionin the blow molding cavity. These processes can be controlled moreeasily and exactly if the blow molding tool arrangement does not executeany further motion.

In a discontinuous blowing process the plastic tube is extrudeddiscontinuously from the extrusion nozzle of an extruder head which ismade as a breaker head into blow molding cavity. During ejection of theplastic tube the distance of the blowing mandrel from the breaker headis increased. The structure of the extrusion blowing machine for thediscontinuous process corresponds largely to that of continuousmachines. In contrast to the known discontinuous process, however, thetube is permanently held and guided in a controlled manner during theproduction process. In this way uncontrolled swinging of the tube isprevented. Moreover holding the tube if necessary can also be used forcontrolled stretching or changing its position.

In the discontinuous process the tube must also be prevented fromrunning onto the surface of the blow molding tool arrangement. To dothis, the rate of change of the distance of the blowing mandrel from thebreaker head is set to be greater than or equal to the ejection speed ofthe plastic tube from the extrusion nozzle.

The process as claimed in the invention in which the plastic tube isguided in a controlled manner during the entire production cycle allowsprocess guidance with any direction of motion of the plastic tube. Whilethe known processes are limited essentially to the vertical extrusiondirection of the plastic tube, guidance of the tube also enables anoblique, even horizontal orientation. For reasons of compatibility withexisting machines however axial alignment is preferred. An axiallyaligned arrangement of the extruder head, the blow molding toolarrangement and the blowing mandrel allows relatively simple control ofthe axial components of motion.

Advantageously the discharge rate of the plastic tube, the extruder headmotion, the adjustment motion of the width of the extrusion nozzle, theblowing mandrel motion and the opening and closing motion of the blowmolding tool arrangement can be adjusted individually and matched to oneanother. This allows implementation of optimized sequences of motionwhich are matched to the requirements of the container which is to beblown, without thus needing to undertake changes on the overall conceptof the process as claimed in the invention. For example, it can beprovided that the plastic tube during the production cycle is tilted inorder to be able to optimally use special geometries of blow moldingcavities and to produce special container geometries.

In one advantageous version of the invention the blow molding toolarrangement comprises at least two mold parts which can be separatedfrom one another, and which are moved for opening and closing the blowmolding tool essentially perpendicular to the extrusion direction out ofan open end position into a closed end position and vice versa. Forexample it can be a blow molding tool which in addition to the moldparts for building up the container body also has a raisable bottompart. For a blow molding tool arrangement fixed in its position theactuating means can likewise be located stationary for the opening andclosing process. Omitting an additional component of motion simplifiesthe mechanical structure and also contributes to reducing the controlcost for the controlled movements of the mold parts.

The advantages of the process were explained using the example of anextruder head with only one extrusion nozzle and one blow molding toolarrangement with only one blow molding cavity. The blow molding toolarrangement can also be for example a single tool or an arrangement oftools with one or more blow molding cavities which are coupled to oneanother. In one advantageous process version an extruder head with amultiple extrusion nozzle tool and a blow molding tool arrangement whichis equipped with a corresponding number of blow molding cavities areused. Moreover there is a number of blowing mandrels which is one ormore times the number of blow molding cavities and which can betransported into the mouths of the blow molding cavities for inflatingthe plastic tubes. In this way, in one blowing cycle with the machineand tool parameters remaining the same, a larger number of hollowbodies, for example plastic bottles, can be produced. In this way thethroughput is increased and the productivity of a multiple blow moldingtool arrangement can be further improved.

An extrusion blowing device which is suited for executing the process asclaimed in the invention for producing hollow bodies, especially plasticbottles, has an extruder head which is located in an equipment framewith an extrusion nozzle, a blow molding tool arrangement with at leastone blow molding cavity, at least one blowing mandrel and at least oneseparation means. As claimed in the invention, on the opposing sides ofthe blow molding tool arrangement there are holding means for theplastic tube. The separating means is provided on the side of the blowmolding tool arrangement facing away from the extruder head.

By providing holding means for the plastic tube on either side of theblowing tool arrangement, the tube is continuously held during theentire production cycle of a container. In this way the prerequisitesfor use of a single blow molding cavity per extrusion nozzle arecreated. Dead times by lateral movements of the blow molding tool meansare avoided. Faulty positions are avoided by the permanent guidance ofthe plastic tube. If it appears to be necessary, the position of thetube can however also be changed in a concerted manner relative to theextrusion direction. In this way for example the requirements of morecomplicated container geometries can be taken into account. All thehollow bodies which are produced with an extrusion nozzle-blow moldingtool arrangement are subject to the same adjustment and tool parameters.Quality differences as a result of tool tolerances of different sizes inseveral different blow molding tools are eliminated. Dead times whichoccur by the lateral displacement of the blow molding tool arrangementrelative to the extruder head can be avoided since the blow molding toolarrangement is aligned essentially only to the transport direction ofthe plastic tube. The inflation of the plastic tube which is located inthe blow molding cavity takes place directly after feed of the blowmolding cavity with the extruded plastic tube. The plastic tube is fixedduring the entire production cycle in a defined position and can nolonger swing around its axis. The extruder head and the blow moldingtool arrangement during the entire extrusion and blowing process remainessentially in a definable and adjustable, geometrical positionalrelationship, and the plastic tube can always be optimally accepted. Inthis way, even for more complicated geometries of the blow moldingcavity, the danger of unintentional pinching of the plastic tube isreduced.

The holding devices for the tube on the one hand are formed by theblowing mandrel and on the other by the extruder head. By using alreadyexisting machine components for the holding functions the structure canbe kept simple and the construction can be kept compact.

In an arrangement which is also advantageous for reasons of space, theblow molding tool arrangement is located between the extruder head andthe blowing mandrel. The blow molding cavity has a mouth on the side ofthe blow molding tool arrangement facing away from the extrusion nozzlein which the blowing mandrel can be transported into the blow moldingcavity. In this arrangement the adjustment and feed movements of thehardware components are limited essentially to movements along thedirection of motion of the plastic tube or essentially vertically. Thisleads to lower mechanical stresses and reduces the vibrations andshaking which occur during operation.

One embodiment of the invention calls for two or more blowing mandrelswhich can be supplied in alternation for the blow molding cavity. Indoing so the blowing mandrels can be located for example next to oneanother and can be moved alternatingly into the correct position. Thetransport paths of the blowing mandrels are very short. In this way thedead times for the feed of the blowing mandrel can be kept short. Onealternative version calls for the blowing mandrels to be mounted on acentral blowing mandrel support, and to be brought into use insuccession by rotation of the blowing mandrel support. For example, theblowing mandrel support can bear two blowing mandrels which are oppositeone another offset by 180°. In this version, after inflating the tubeand opening the blow molding tool, the blowing mandrel support is turnedby 180°. The second blowing mandrel is thus already prepared forinflation of another tube section, while the hollow body on the firstblowing mandrel waits for its removal. It goes without saying thatrotary blowing mandrel supports with 3, 4 or more blowing mandrels canalso be provided. The angle by which the blowing mandrel support mustcontinue to be turned then results from the division of 360° by thenumber of blowing mandrels.

Advantageously, on each blowing mandrel there are calibration means withwhich during the blowing process the opening of the blown hollow bodycan be calibrated. In this way a time-consuming finishing step can beeliminated.

To prevent the plastic tube from running against hardware components orsagging during the extrusion and blowing cycle, there are actuatingmeans with which the relative distance between the extruder head and theblow molding tool arrangement can be adjusted. One advantageous versioncalls for the extruder head to be connected to the actuating means andthe distance relative to the stationary blow molding tool arrangement tobe adjustable. This arrangement has the advantage that on the blowmolding tool arrangement precautions need be taken essentially only forthe opening and closing of the mold parts. This simplifies the sequencesof motion and the control cost.

The extruder head can be made for continuous extrusion of the plastictube. In this version the change in the distance between the extruderhead and the blow molding tool arrangement takes place at least with theextrusion speed of the plastic tube. In one alternative version of theinvention the extruder head is made as a breaker head for discontinuousejection of the plastic tube. In this version, the distance of theblowing mandrel can be adjusted at least with the ejection rate of theplastic tube relative to the blow molding tool arrangement.

Since on both sides of the blow molding tool arrangement there areholding means for the plastic tube, the alignment of the extrusionnozzle, the blow molding tool arrangement and the blowing mandrel ormandrels can be selected at will. For reasons of compatibility withexisting devices and system components, however an arrangement ispreferred in which the extruder head has an essentially verticallyaligned extrusion nozzle and the blow molding tool arrangement and theblowing mandrel or mandrels are arranged vertically under one another.The vertical arrangement also uses the action of gravity on the extrudedplastic tube which is stabilizing to a certain extent.

The blow molding tool arrangement comprises at a least two mold partswhich can be separated from one another and which can be moved foropening and closing essentially perpendicular to the extrusion directionof the plastic tube out of an open end position into a closed endposition and vice versa. For example, it can be a blow molding toolwhich in addition to the mold parts for building up a container bodyalso has a raisable bottom part. For a blow molding tool arrangementwhich is fixed in its position the actuating means for the opening andclosing process can likewise be located stationary. Omitting anadditional movement component simplifies the mechanical structure andalso contributes to reducing the control cost for controlled movementsof the mold parts.

For reasons of higher throughput, it is advantageous if the extruderhead has several extrusion nozzles and the blow molding tool arrangementis equipped with a corresponding number of blow molding cavities.Preferably there are a number of blowing mandrels which is one or moretimes the number of blow molding cavities. Aside from the higherthroughput and the improved productivity of the multiple blow moldingtool, in this version a larger number of hollow bodies, for example,plastic bottles, can be produced with uniform machine and toolparameters in one blowing cycle. This has advantages with respect to theuniformity of the quality of the products made.

Other advantages and features of the invention result from the followingdescription with reference to the schematics of one embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic of an extrusion blowing machine of the priorart;

FIG. 2 shows a diagram of an arrangement of an extruder head, a moldtool and a blowing mandrel as claimed in the invention; and

FIGS. 3-11 show schematics for explanation of the process as claimed inthe invention.

DETAILED DESCRIPTION

The extrusion blowing machine of the prior art shown only schematicallyin FIG. 1 is labelled overall with reference number 1. The structure ofthese long-stroke extrusion blowing machines has been known for a longtime and is described for example in Blow Molding Handbook, edited byDonald V. Rosato and Dominick V. Rosato, 1989, ISBN 1-56990-089-2,Library of Congress Catalog Card Number 88-016270. FIG. 1 is thereforelimited to the components of the extrusion blowing machine 1 which areabsolutely essential for understanding. This embodiment is a two-stationblowing machine, as is also offered by the applicant. It has anextrusion unit 2 and two blowing stations 12, 13. The extrusion unit 2comprises an extruder 3 for the plastic granulate and an extruder head 4which is connected to it and which has at least one extrusion nozzle 5.The blowing stations 12, 13 each have one blowing head with a blowingmandrel. Each blowing station 12, 13 is equipped with a blow moldingtable 14, 15 in which blow molding tools 6 are mounted. The blow moldingtools 6 each surround a blow molding cavity 7 which corresponds to theshape of the hollow body which is to be produced, for example a bottle.The blow molding cavities 7 on their top facing the extruder head 4 havea mouth 8. The blow molding tables 14, 15 can be moved in alternationout of their side end positions in the blowing stations 12, 13 into aposition in which the mouth 8 of the blow molding tool 6 is axiallyflush with the output of the extrusion nozzle 5. The lateraldisplacement of the blow molding tables 14, 15 takes place essentiallyperpendicular to the lengthwise extension of the extruder 3.

The plastic granulate which is supplied via the extruder 3 is melted inthe extruder 3 and/or in the extruder head 4 and is extruded from theextrusion nozzle 5 as a continuous tube. The tube can be extruded in oneor more layers. To do this there can also be other extruders whichtransport the required different plastic materials to the extruder head4. The blow molding tables 14, 15 with the blow molding tools 6 aremoved in alternation out of their end positions into the blowingstations 12, 13 laterally to under the extruder head 4, the blow moldingtools 6 are opened and a piece of the extruded tube is retrieved.Afterwards the respective blow molding table 14, 15 is moved back againinto its end position in the blowing station 12 and 13. There, thehollow body is inflated using a blowing mandrel which has beentransported into the cavity 7 through the mouth 8. The finished hollowbody is ejected and the cycle repeated. While a tube is being inflatedin one blow molding station 12, the blow molding table 15 of the secondblowing station 13 is moved laterally to under the extrusion head 4 inorder to retrieve another piece of the extruded tube. In this waycontinuous operation is possible.

FIG. 2 schematically shows an arrangement of the hardware componentsimportant to the invention. Here the designations from FIG. 1 wereretained in order to enable direct comparison. Reference number 4 inturn labels the extruder head which has the extrusion nozzle 5.Reference number 6 stands for the single blow molding tool of theextrusion blowing device which in this embodiment comprises two blowmold halves 8, 9 which are shown in the opened state. The two blow moldhalves 8, 9 border the blow molding cavity 7 with a mouth 10 which islocated on the side of the blow molding tool facing away from theextrusion nozzle 5. Proceeding from a practical arrangement of thehardware components, the mouth 10 of the blow molding cavity 7 is on thebottom of the blow molding tool 6. A blowing mandrel which is labelledwith reference number 11 is mounted on the blowing mandrel support 16.In this embodiment the blowing mandrel support 16 has two blowingmandrels 16 which can be moved alternately to under the mouth 10 of theblow molding cavity 7 by turning the blowing mandrel support 16 by 180°.The extruder head 4 and the sole blow molding tool 6 are arranged suchthat the axis of the blow molding cavity 7 and the output of theextrusion nozzle 5 on the extruder head 4 are axially flush with oneanother. In the embodiment shown, the blowing mandrel pair 11 is alsoarranged such that it is flush with the axis of the blow molding cavity7. This however is not a compelling requirement. It goes without sayingthat for an eccentrically arranged mouth of the blow molding cavity theblowing mandrel can be accordingly offset laterally. But it is importantto the arrangement as claimed in the invention that the extruder head 4and the blow molding tool 6 are flush with one another in the axialdirection. Reference number 17 labels a blade which is used to cut offthe individual blown hollow bodies.

The arrows shown in FIG. 2 indicate the adjustability of the individualhardware components. Thus, the extruder head 4 can be adjustedessentially only with respect to its height in order to change thedistance to the blow molding tool 6 during the extrusion and blowingprocess. For the required base setting and fine adjustment however ithas all degrees of freedom. The blow mold halves 8, 9 of the blowmolding tool 6 can only be moved laterally out of an open end positioninto a closed end position and vice versa. In the embodiment shown, theblow molding tool 6 does not have vertical adjustability. The blowingmandrel pair 11 which is mounted on the blowing mandrel support 16 isvertically adjustable in order to be able to be transported into themouth 10 of the blow molding cavity 7 and withdrawn again. In order tobe able to use the blowing mandrels 11 in alternation, the blowingmandrel support 16 can also be turned.

FIGS. 3 to 11 serve to explain the process for production of a plastichollow body. FIG. 3 shows the automatic cycle beginning with the statein which the blow molding tool 6 is closed. The tube T which has beencontinuously extruded from the extrusion nozzle 5 of the extruder head 4is indicated by T. One of the two blowing mandrels 11 is transportedinto the mouth 10 of the blow molding cavity 7. Reference number 17stands for the blade which is inactive in this state. In the state shownin FIG. 3 a tube which is located in the blow molding cavity is inflatedaccording to the blow molding cavity. During the blowing process theextruder head 4 is continuously raised and the vertical distance to theblow molding tool is continuously increased. This is indicated in FIG. 4by the lengthening of the extruded tube T. If the extruder head israised with a speed which is greater than the extrusion speed of theplastic tube, the tube is pulled out of the extrusion nozzle andstretched, and its wall thickness decreases. During raising of theextruder head 4 if necessary a wall thickness control program can be runin which the wall thickness of the tube can be changed to the desiredextent by varying the gap width of the extrusion nozzle. A finish-blownbottle B hangs on the second blowing mandrel 11 which is located outsidethe blow molding cavity. In this position it could be subjected forexample to an aftercooling process or other finishing which is notdetailed.

The end of the blowing process is shown in FIG. 5. The extruder head 4is moved still further from the blow molding tool 6 and is raisedfurther. The inflated bottle which is located in the blow molding cavity7 is vented by the blow molding tool 6. The bottle B hanging on thelower blowing mandrel 11 is removed. After this process, the blow moldhalves 8, 9 of the blow molding tool 6 are raised; this is indicated inFIG. 6. The extruder head 4 is still being raised in doing so. After thebottle B which has been inflated in the blow molding cavity has beencompletely removed from the blow molding cavity 7, the movement of theextruder head 4 is stopped and vice versa. As is shown in FIG. 7, theextruder head 4 with the extruded tube piece T and the finish-blownbottle B which is still connected to it is moved down in the directionof the blow molding tool 6. The blowing mandrel 11 which is mounted onthe blowing mandrel support 16 is likewise lowered.

FIGS. 6 and 7 clearly show that the extruded tube T even with the blowmolding tool 6 opened is held in a position which is aligned in anaxially defined manner. Because the tube is still connected to thefinish-blown container B, the tube on the one hand is fixed by theextrusion nozzle 6 and on the other via the blowing mandrel 11. In thisway swinging of the tube T is reliably prevented. The rate of loweringof the extrusion head 4 and of the blowing mandrel 11 takes placeadvantageously synchronously and corresponds at least to the extrusionspeed of the tube T. By a definable difference of lowering speeds thecontinuously extruded tube T can be stretched to the desired extent. Theaxially aligned arrangement of the extruder head 4, of the blow moldingtool 6 and of the blowing mandrel 6 also allows relatively simplecontrol of the axial components of motion. Advantageously the exit speedof the plastic tube T, the motion of the blowing mandrel 11 and theadjustment motion of the width of the extrusion nozzle 5 can be adjustedindividually and matched to one another. This allows implementation ofoptimized motion sequences which are matched to the requirements of thecontainer B which is to be blown without in this way needing toundertake changes in the overall concept of the axially aligned motion.

FIG. 8 shows the state in which the blowing mandrel support 16 hasreached its lowest position. At this point, the halves of the blowmolding tool 6 are closed again in order to inject a new tube section inthe mold cavity. Shortly before the blow molding tool 6 is completelyclosed, the blade 17 is supplied laterally in order to separate thefinish-blown bottle B from the scrap piece projecting out of the mouthof the blow molding cavity. This is indicated in FIG. 8 by a doublearrow. The extruder head 4 in the meantime has again reversed itsdirection of motion and is raised again. After separation, the blowingmandrel support 16 is turned in order to align the second blowingmandrel 11 to the mouth of the blow molding cavity. During rotation ofthe blowing mandrel support 16 it can be supplied to the blow moldingtool 6. The rotation and vertical adjustment of the blowing mandrelsupport 16 are shown in FIG. 9 by the corresponding arrows. During thisprocess the extruder head 4 is raised again. FIG. 10 shows the state inwhich the rotation process of the blowing mandrel support 16 has beencompleted and the blowing mandrel 11 has reached its correct strokeposition. Afterwards it is transported into the mouth 10 of the blowmolding cavity 7. In doing so the later opening of the bottle to beinflated is calibrated. Preliminary blowing can be started duringtransport of the blowing mandrel 11 into the blow molding cavity 7. Theextruder head 4 is raised further in doing so. In FIG. 11 the blowingmandrel 11 is finally transported into the blowing mandrel cavity of theblow molding tool 6 and the production cycle starts again from thefront. FIG. 11 corresponds to FIG. 3 here.

The schematics show an extruder head with only one extrusion nozzle anda blow molding tool with only one blow molding cavity. It goes withoutsaying that the described arrangement and the described process can alsobe used in extrusion blowing devices with multiple nozzle tools andmultiple blow molding tools or arrangements of single and/or multipleblow molding tools. The number of blowing mandrels is matched to thenumber of blow molding cavities here.

The invention has been explained using the example of a continuousextrusion blowing process and a corresponding devised device with avertical arrangement of the extruder head, of the blow molding tool, andof the blowing mandrels. It goes without saying that the hardwarecomponents can also be arranged in a horizontal or any alignmentaccording to the extrusion direction. The process as claimed in theinvention can also be used in a discontinuous extrusion blowing processand accordingly a discontinuous extrusion blowing machine can also beproduced. The decisive factors in a discontinuous process are likewiseproviding holding means for the tube on either side of the blow moldingtool arrangement and the sequence of the arrangement of the extruderhead, the blow molding tool arrangement and the blowing mandrel. It isimportant to the invention that the extruded tube is held in acontrollable position during the entire production cycle and the tube iscut off only after inflation and removal of the container from the mold.The point of separation is located on the side of the blow molding toolarrangement facing away from the extruder head.

It will be appreciated by those skilled in the art that the presentinvention can be embodied in other specific forms without departing fromthe spirit or essential characteristics thereof. The presently disclosedembodiments are therefore considered in all respects to be illustrativeand not restricted. The scope of the invention is indicated by theappended claims rather than the foregoing description and all changesthat come within the meaning and range and equivalence thereof areintended to be embraced therein.

The invention claimed is:
 1. A device for producing hollow bodies,comprising: an extruder head which is located in an equipment frame withan extrusion nozzle, a blow molding tool arrangement with a blow moldingcavity, and at least one blowing mandrel, the extruder head, the blowmolding tool arrangement and the at least one blowing mandrel beingarranged in an axial relationship and at least one separation means fora plastic tube, wherein on opposing sides of the blow molding toolarrangement there are holding means for the plastic tube and theseparation means is located on a side of the blow molding toolarrangement facing away from the extruder head, and an activator withwhich a relative axial distance between the extruder head and an endface of the blow molding tool arrangement can be adjusted.
 2. Device asclaimed in claim 1, wherein the holding means for the plastic tube arethe extruder head and the blowing mandrel.
 3. Device as claimed in claim1, wherein the blow molding tool arrangement is located between theextruder head and the blowing mandrel, and the blow molding cavity on aside of the blow molding tool arrangement facing away from the extrusionnozzle has a mouth through which the blowing mandrel can be transportedinto the blow molding cavity.
 4. Device as claimed in claim 3, whereinfor each blow molding cavity there are two or more blowing mandrelswhich are transported in alternation into the blow molding cavity. 5.Device as claimed in claim 3, wherein the blowing mandrels are mountedon a central blowing mandrel support for use in succession by rotationof a blowing mandrel support.
 6. Device as claimed in claim 1, whereineach blowing mandrel is provided with a calibration means with which anopening of a hollow body can be calibrated during a blowing process. 7.Device as claimed in claim 1, wherein the actuating means are connectedto the extruder head.
 8. Device as claimed in claim 1, wherein theextruder head is made for continuous extrusion of the plastic tube. 9.Device as claimed in claim 1, wherein the extruder head is made as abreaker head for discontinuous ejection of the plastic tube, and adistance of at least one blowing mandrel at least with an ejection speedof the plastic tube can be adjusted relative to the blow molding toolarrangement.
 10. Device as claimed in claim 1, wherein the extruder headhas an essentially vertically aligned extrusion nozzle and the blowmolding tool arrangement and at least one blowing mandrel are arrangedvertically under one another.
 11. Device as claimed in claim 1, whereinthe blow molding tool arrangement comprises at least two mold partswhich can be separated from one another and which are moved for openingand closing the blow molding tool essentially perpendicular to anextrusion direction of the plastic tube out of an open end position intoa closed end position and vice versa.
 12. Device as claimed in claim 1,wherein the extruder head has several extrusion nozzles, the blowmolding tool arrangement is equipped with a corresponding number of blowmolding cavities, and there is a number of blowing mandrels which is oneor more times the number of blow molding cavities.